Cerium based abrasive material and method for producing cerium based abrasive material

ABSTRACT

Regarding a cerium oxide-based abrasive containing cerium oxide as a main component and abrasive particles with an average particle diameter of 0.2 to 3.0 μm, the present invention provides a cerium-based abrasive containing coarse particles of 10 μm or larger in a concentration of 1000 ppm or lower (by weight) or magnetic particles in a concentration of 1000 ppm or lower (by weight). The coarse particles or the magnetic particles are particularly preferable to exist in a concentration of 300 ppm or lower (by weight) . Further, by controlling an average value of the specific surface area of the abrasive particles to be within 0.5 to 30 m 2 /g, the resulting abrasive is provided with a high cutting property and is capable of forming a polished face with high precision. The production method of such cerium-based abrasives comprises control being the concentration of the coarse particles and the classification point and repeated classification. The control of the magnetic particle concentration is made possible by utilization of a filter of a magnetic material and alteration of pulverization media, which are either solely or properly combined with each other to be performed.

TECHNICAL FIELD

[0001] The present invention relates to a cerium-based abrasivecontaining cerium oxide as a main component and excellent in polishingprecision and cutting property as well.

BACKGROUND ART

[0002] Recently, a cerium-based abrasive containing cerium oxide (CeO₂)has been used for polishing a variety of glass materials. Especially, acerium-based abrasive has been employed for polishing from conventionalcommon plate glass materials to glass materials today to be used forelectric and electronic apparatuses, for example, glass for magneticrecording media such as hard disks, glass substrates of liquid crystaldisplays (LCD) and its application field is widened.

[0003] The cerium-based abrasive is composed of abrasive particlescontaining cerium oxide (CeO₂) particles as a main component. Thecerium-based abrasive can widely be classified into a high ceriumabrasive and a low cerium abrasive depending on the content of ceriumoxide. The high cerium abrasive contains at least 70% by weight ofcerium oxide in relation to the whole amount of the rare earth oxides(hereinafter abbreviated as TREO) and is an abrasive containing acomparatively large amount of cerium oxide, whereas the low ceriumabrasive is an abrasive containing cerium oxide in the content asrelatively low as about 50% by weight in relation to TREO. Although thecontent of cerium oxide and the raw materials of these cerium-basedabrasives are different, the production steps after raw materialpreparation are not so much different.

[0004]FIG. 1 shows the production steps of these cerium-based abrasives.The raw materials to be used for the high cerium abrasive are rare earthchlorides obtained by chemically treating and concentrating a rare earthore so-called monazite. On the other hand, conventionally usually usedas the raw materials of the low cerium abrasive is a bastnasiteconcentrate obtained by dressing the rare earth ore so-called bastnasiteand recently, raw materials mainly used are derived from rare earthoxides or rare earth carbonates synthesized using the bastnasite ore andrelatively economical complex ores produced in China. In the steps afterraw material preparation, both are produced by chemically treating theraw materials (by the wet treatment), filtering, drying them, andfurther roasting them and pulverizing and sieving the obtained rawmaterials. The particle diameter of the abrasive particle constitutingan abrasive is 0.2 to 3.0 μm on the bases of the average particlediameter, although depending on the purposes from the rough finishing tothe final finishing, and it is controlled by adjusting the temperaturein the foregoing production steps and the roasting step and adjustingthe pulverization and the classification steps.

[0005] By the way, one reason why a cerium-based abrasive has widelybeen employed is that a large quantity of glass can be removed byabrasion within a relatively short time to obtain a high polishing valuein addition to that a polished face with high precision can be obtained.In this case, regarding the polishing mechanism of the cerium-basedabrasive, there are not necessarily any clear established theories,however, it is said that the fluorine component contained in an abrasivetakes a significant role. That is, in addition to the mechanicalpolishing effect by cerium oxide, it is said that also the chemicalpolishing function is simultaneously caused as follows: the fluorinecomponent contained in the abrasive reacts with the glass face tofluorinate the glass and accelerate corrosion of the glass surface.Therefore, regarding the cerium-based abrasive, it is supposed to bepossible to exert the excellent polishing properties when both of themechanical function and the chemical function are sufficientlyperformed.

[0006] As the first standard to produce an abrasive with excellentpolishing properties, first of all, it is required for the abrasive tobe free from abnormally grown abrasive particles and to have evenness inthe particle diameter distribution. Therefore, in the production stepsof the cerium-based abrasive, a variety of countermeasures are performedso as to suppress the abnormal particle growth of the abrasiveparticles. For example, in the chemical treatment steps, a raw materialpulverized with a mineral acid such as hydrochloric acid, sulfuric acid,and the like is treated. That is for dissolving and removing alkalimetals, e.g. sodium, and alkaline earth metals contained as impuritiesin the raw material with mineral acids since these alkali metals andalkaline earth metals cause the abnormal particle growth in the roastingstep thereafter.

[0007] Further, in addition to the control in these production steps,regarding produced abrasives, product inspection is randomly performedto investigate the average particle diameter and the particle diameterdistribution to investigate the existence of coarse particles owing tothe abnormal particle growth.

[0008] Excellent abrasives have been supplied ever before through theabove described control of the particle diameter distribution ofabrasive particles in the production steps and the fluorineconcentration and product inspection.

[0009] However, taking the demands for the cerium-based abrasive in thefuture into consideration, it is natural to be desired to developfurther excellent abrasives. Especially, since further integration to ahigh density is required in an industrial field of a glass substrate forhard disks, LCD and the like and for that, it is required to obtain anabrasive which not only is capable of forming a polished face withextremely high precision but also has a high cutting property to carryout polishing to a prescribed extent at a high speed.

[0010] Hence, the present invention aims to provide a cerium-basedabrasive capable of forming a polished face with precision higher thanthat a conventional method has ever achieved and having an excellentcutting property and a new standard and to provide a production method.

DISCLOSURE OF THE INVENTION

[0011] The inventors of the present invention have made investigation indetails in polishing properties of conventional cerium-based abrasivesand found a problem that scratches are sometimes formed in the polishedface even in the case of using a conventional abrasive with a finelyminiaturized average particle size and of which the particle diameterdistribution is found no problem in a product inspection. Then, avariety of investigations into the causes of the occurrence of suchscratches have been performed and consequently, the following twoproblems are found in the conventional abrasives which are regarded notto have any problem in the particle diameter distribution by the abovedescribed inspection method and thus the present invention is achieved.

[0012] The first problem in the conventional cerium-based abrasives isthe existence of coarse particles in an extremely slight amount, whichare inevitably contained by a conventional production method and whichare impossible to be detected by a conventional inspection method. Inthis case, the coarse particles- in the present invention mean particleshaving a particle diameter several times as large as the averageparticle diameter of the abrasive particles composing an abrasive andhaving a particle diameter within a range in which they can not bedetected by the particle diameter distribution by a conventionalinspection method and within a range of 10 to 50 μm or more.

[0013] The inventors of the present invention have thought it isnecessary to clarify the relation between the coarse particleconcentration and the polished face even if the amount is extremelyslight in order to obtain an abrasive with higher precision ever before.From such a viewpoint, the inventors of the present invention haveenthusiastically investigated and consequently found that even if thosefound having no problem by a conventional inspection method containcoarse particles with a diameter of 10 μm or larger in 1,500 ppm or moreby weight.

[0014] The inventors of the present invention have then found as a firstinvention that an abrasive can be provided corresponding. to theapplications by optimizing the coarse particle concentration accordingto the results of production of a variety of cerium-based abrasives withdifferent coarse particle concentrations by production methods performedby variously modifying a conventional production method as describedsomewhere later and investigation of the frequency of the occurrence ofthe scratches in the polished face.

[0015] In other words, the first invention of the present application isa cerium oxide-based abrasive containing cerium oxide with an averageparticle diameter of 0.2 to 3.0 μm as a main component, wherein thecerium oxide-based abrasive contains coarse particles with a particlediameter of 10 μm or larger in a concentration of 1,000 ppm or lower byweight.

[0016] The cerium-based abrasive according to the first invention is onecontaining the coarse particles in a lowered concentration as comparedwith that of a conventional one and such an abrasive having 1,000 ppm orlower by weight concentration of the coarse particles of 10 μm or largeris suitable for polishing the glass face of a Braun tube and a CRT. Byusing such an abrasive, polishing the glass face of these products canprovide a polished face with desired precision without formingscratches.

[0017] Further, according to the findings of the inventors of thepresent invention, it is confirmed that as the concentration of thecoarse particles is lowered, the scratch formation can be suppressedmore to obtain a polished face with desired precision. Especially,regarding the requirement for a polished face with extremely highprecision for the finishing polishing of a glass substrate or the likefor a hard disk and a LCD, today, a polished face scarcely havingscratches has been required. It is therefore preferable to use anabrasive containing coarse particles with 10 μm or larger particle sizein the concentration of 300 ppm by weight or lower in polishing at suchhigh precision.

[0018] The second problem of a conventional cerium-based abrasive is theexistence of the magnetic particles composed of magnetic metals of iron,nickel, and the like. Such magnetic particles are supposed to becontained in raw materials from the beginning or mixed during theproduction steps. Especially, in the production steps, contaminationtakes place supposedly attributable to the constituent materials of awet pulverize, a drier, a roasting apparatus, a dry pulverize, and thelike in the steps such as a wet pulverization step, a drying step, aroasting step, a dry pulverization step. The reason why the magneticparticles become causes of the occurrence of the scratches is supposedto be that the difference of the hardness between the magnetic particles(metal particles) and the abrasive (a metal oxide of such as ceriumoxide) makes uniform polishing impossible.

[0019] The inventors of the present invention have made investigationsof the relation between the content of the magnetic particles and thefrequency of scratch occurrence based on the above described findingsand have thought it is possible to obtain a highly precise cerium-basedabrasive with no probability of causing scratches by defining theconcentration of the magnetic particles within a prescribed range andachieved the second invention of the present application.

[0020] The second invention of the present application is a ceriumoxide-based abrasive containing cerium oxide with an average particlediameter of 0.2 to 3.0 μm as a main component, wherein the ceriumoxide-based abrasive contains magnetic particles in a concentration of1,000 ppm or lower (by weight).

[0021] The cerium-based abrasive according to the second invention iswherein the content of the magnetic particles of a conventionalcerium-based abrasive is lowered to suppress the concentration of themagnetic particles to 1,000 ppm or lower. The reason why theconcentration of the magnetic particles is suppressed to 1,000 ppm orlower is because the concentration of the magnetic particles of aconventional cerium-based abrasive causing the scratches is found to be1,500 ppm or higher by weight and the restriction is based on theconsequent finding by investigations that the occurrence of scratchescan reliably be suppressed to 1,000 ppm or lower.

[0022] The inventors of the present invention have confirmed that as theconcentration of magnetic particles is lowered, the occurrence of thescratches is suppressed more to obtain the polished face with highprecision. The abrasive containing magnetic particles in a concentrationof 1,000 ppm or lower by weight is suitable, for example, for polishingglass face of a Braun tube and a CRT. On the other hand, regardingfinishing polishing of a glass substrate or the like for a hard disk anda LCD, since extremely high precision of the polished face has todaybeen required, the requirement can be satisfied by further decreasingthe concentration of the magnetic particles and it is preferable to usethose containing magnetic particles in a concentration of 300 ppm byweight or lower. Further, especially for a hard disk, if magneticparticles remain on the substrate surface after polishing, it causes asignificant problem in magnetic recording and reproduction systems toresult in deterioration of the reliability of the hard disk.Consequently, by using such an abrasive with a decreased concentrationof magnetic particles of the present invention, the quality of a harddisk produced can be improved.

[0023] As described above, cerium-based abrasives according to thepresent invention contain coarse particles and magnetic particles incontents within respectively prescribed ranges, and these cerium-basedabrasive can be said to be highly precise abrasives with no probabilityof causing scratches on the polished face.

[0024] Further, the inventors of the present invention have found acerium-based abrasive having an excellent cutting property and capableof forming a polished face with high precision not only by controllingthe concentration of the coarse particles and the concentration of themagnetic particles but also by controlling the specific surface area towithin a range of 0.5 to 30 m²/g.

[0025] If the specific surface area is smaller than 0.5 m²/g, theabrasive particles become so large owing to excess proceeding ofsintering that it is supposed scratches are caused at the time ofpolishing. Further, if the specific surface area is larger than 30 m²/g,the abrasive particles become so small owing to the insufficient degreeof sintering that it is supposed the cutting property is too lowered.

[0026] As described above, a cerium-based abrasive comprising abrasiveparticles with a specific surface area within a prescribed range andhaving a decreased concentration of coarse particles and a decreasedconcentration of magnetic particles is capable of forming the polishedface with high precision and taking an expected vast expansion ofapplications of a cerium-based abrasive in the future intoconsideration, it is necessary to stably produce a large quantity of theabrasive. The inventors of the present invention have reviewed theconventional production steps of a cerium-based abrasive and found thatthe concentration of coarse particles, the concentration of magneticparticles, and the specific surface area of the abrasive particles caneasily be controlled by altering the production conditions. In thiscase, the conventional steps for producing a cerium-based abrasive canwidely be divided into a step of forming a slurry by mixing an abrasiveraw material and a dispersing medium, a step of pulverizing the abrasiveraw material by treating the slurry by a wet pulverize, a step ofroasting the abrasive raw material subjected to the pulverization afterfiltration and drying, and a step of again classifying the abrasive rawmaterial after it is subjected to the roasting followed byrepulverization.

[0027] A method for lowering the concentration of coarse particles,which is the first characteristic of the present invention, comprisesthe following two improvements in the classifying step.

[0028] The first improvement is to lower the concentration of the coarseparticles by setting the classifying point to 0.5 to 15 μm. In thiscase, the classifying point denotes the particle diameter to be aboundary of particles to be separated by a classifying apparatus and itgenerally means the particle diameter value at which the partialclassification efficiency (the particle amount in the separated fineparticle side to the particle amount before the classification) becomes50%. The classifying point is generally corresponding to the operationconditions (e.g. the air delivery, the rotation speed, and the like inthe case of a wind type classifying apparatus) and in the presentinvention, the classification point is fixed to carry out theclassification treatment by setting the operation conditions of theclassifying apparatus. The reason why the range of the classificationpoint is set from 0.5 to 15 μm is that in the case of 15 μm or larger,the concentration of coarse particles cannot be lowered and on the otherhand that even in the case of setting the classification point to be 0.5μm or smaller, it becomes difficult to set the operation conditions ofthe classifying apparatus corresponding to the setting. Further, takingthe production efficiency of an abrasive into consideration, theclassification point especially preferable is within a range from 1 to10 μm.

[0029] Incidentally, the classification treatment involving suchalteration of classification point does not restrict the models ofclassifying apparatuses. Consequently, the treatment is made possible byany types of apparatuses, e.g. so-called a dry classifying apparatussuch as a wind type classifying apparatus and so-called a wet typeapparatus such as a liquid cyclone.

[0030] The second method for lowering the concentration of coarseparticles is that re-classification of an abrasive after classificationis carried out at least once. That is based on the consideration thatthere is possibility of occurrence of contamination of coarse particleswith the size equal to or larger than the classification point in theabrasive by only once classification even if the classification point islimited. By carrying out re-classification, the concentration of thecoarse particles in the abrasive can be lowered. The number of times torepeat the re-classification is sufficient to be about once taking theproduction efficiency of the abrasive into consideration. Incidentally,the re-classification is preferable to be carried out in combinationwith the above described control of classification point, that is, theclassification point is restricted within a range of 0.5 to 15 μm.Consequently, it is made easy to produce an abrasive having theconcentration of coarse particles in 300 ppm or lower and possible to beused for finishing polishing. Incidentally, the classification point atthe time of re-classification in that case may be set at the same valueof the classification point at the time-of first classification.

[0031] On the other hand, as a method for lowering the concentration ofmagnetic particles, the following three are available. A first techniqueto lower the magnetic particles of an abrasive comprises a step ofpassing a slurry treated by a wet type pulverize through a magneticmaterial magnetized by excitation. The reason for the removal ofmagnetic particles from an abrasive raw material in the slurry state isbecause if being in the slurry state, the particles are scarcelyagglomerated and the magnetic particles are made easy to move by themagnetic field, so that the magnetic particles can efficiently becollected. more practically, magnets are arranged in the circumferenceof a filter and the magnets are excited to apply a magnetic field to thefilter part to magnetize the filter and then a slurry of the abrasivematerial is passed through the filter. In this case, electromagnets arepreferable to be employed as the magnets to magnetize the magneticfilter and the intensity of the magnetic field to be generated ispreferable to be within a range from 0.1 to 2.0 T magnetic flux density.In the case of 0.1 T or lower, small magnetic particles cannot becollected, whereas in the case of 2.0 T or higher, the operation cost ofthe magnets is increased and additionally it becomes difficult to removethe attracted magnetic particles adhering to the filter at the time ofmaintenance to result in decrease of the productivity. The number of thetimes to repeat the filtration of the abrasive slurry is notparticularly restricted, however by setting the number to be a pluralityof times, the concentration of the magnetic particles can further bedecreased.

[0032] Incidentally, the models of a wet type pulverize to be employedin this case are not particularly restricted, however, applicable are,for example, a wet type ball mill, a bead mill, an attriter and thelike. Further, at the time of carrying out wet pulverization of theabrasive raw material, it is necessary to make the abrasive raw materialbe a slurry by mixing it with a dispersing medium, and procedure at thetime includes a case carrying out the steps of previously mixing theabrasive raw material with a dispersing medium to produce a slurry andthen pulverized by loading a wet type pulverize with the slurry andbesides the case, also includes a case of carrying out the steps ofloading a wet type pulverize with an abrasive raw material and adispersing medium to start pulverization and make the abrasive rawmaterial be a slurry at the initial period of the pulverization. Thesecases are similarly applicable for the following production methods.

[0033] As a second technique to lower the magnetic particles of anabrasive includes steps of pulverizing the abrasive raw material using apulverization medium made of a non-magnetic material with which a wettype pulverize is filled to pulverize a slurry to be pulverized. Thepulverization medium is an object which moves interlockingly with themovement (rotation, vibration) of the pulverize while being packed inthe pulverize and consequently performs pulverization function andball-like ones are used for the above described wet type ball mill orthe like. The material to be used for the medium is generally iron or awear resistant steel in consideration of the cost and the pulverizationefficiency.

[0034] In this case, as described above that the cause of thecontamination of the abrasive with magnetic particles is attributed tothe raw material pulverization step among the production steps, that issupposedly attributed to that wear or pulverization of the pulverizationmedium is caused during the pulverization step and it becomes one ofcauses of contamination with magnetic particles. The second method aimsto inhibit generation of magnetic particles by using a non-magneticmaterial for the material of the pulverization medium and consequentlyto lower the concentration of magnetic particles in the abrasive. Hence,taking the intrinsic function of pulverizing a raw material intoconsideration, it is preferable to use a non-magnetic and hard materialsuch as zirconia or alumina for the constituent material of thepulverization medium. Incidentally, in the case where a non-magneticmaterial for the pulverization medium, it is preferable to use a hardnon-magnetic material for the inner parts of a pulverizer and the innerfaces of pipes and tubes to be brought into contact with the slurry inthe pulverize.

[0035] As a third technique to decrease the magnetic particles in anabrasive, an abrasive raw material after roasting is passed through theperipheral part of a tubular body, a plate-like body, and a rod-likebody made of a magnetized magnetic material. Among the abrasiveproduction steps, the step is the treatment for the abrasive material inform of almost the final product shape in terms of the composition afterthe roasting and pulverization steps and before classifying step and thedry treatment in contrast with the treatment for the slurry state. Thethird method is effective to remove mixed magnetic particles derivedfrom the constituent materials of the roasting furnace or the pulverizein the roasting step or the pulverization step after the roasting.Incidentally, the dry type magnetic particle removal step is a treatmentfor the abrasive raw material after the roasting and may be carried outafter dry type pulverization immediately after the roasting or beforethe classification treatment and may be carried out at any timing afterthe dry pulverization or after the classification treatment. Further, apractical embodiment of the method includes that the abrasive rawmaterial after the roasting is passed through the inside of a tubularbody or a box body magnetized by excitation, that the abrasive rawmaterial is brought into contact with magnets arranged in atransportation passage for the abrasive raw material after the roasting,and that the abrasive raw material is passed between two magnetizedmetal plates or metal rods. Further, the magnetic flux density of amagnetic material to be magnetized is preferably within a range from 0.1to 2.0 T according to the same reason as already described in the caseof the magnetic filter.

[0036] By the above described three methods for decreasing the magneticparticle concentration, magnetic particles can efficiently be removedwithout requiring additional installation of large scale facilities anda cerium-based abrasive with a high quality can be produced at a lowcost. Although the magnetic particle removal treatments are of courseeffective even if the respective treatments are carried out separately,the concentration of magnetic particles can further efficiently bedecreased by combining two or all three methods.

[0037] Hence, regarding a cerium-based abrasive as described above, acerium-based abrasive capable of forming a polished face with aprecision and having excellent cutting property can be obtained not onlyby controlling the concentration of coarse particles and theconcentration of magnetic particles but also by controlling the specificsurface area to be within a range from 0.5 to 30 m²/g. As describedabove, in order to keep the specific surface area of an abrasive withinthe above described range, it is important to control the sinteringconditions. Although depending on the sintering method and the particlediameter of the abrasive raw material before the sintering, thesintering conditions are preferably controlled to be 600 to 1100° C. ofsintering temperature and 1 to 60 hours of sintering duration.

[0038] Incidentally, in the above described production method of thecerium-based abrasive, it is required to disperse a raw material in adispersion medium at the time of wet pulverization of the raw material,an organic solvent may be usable for the dispersing medium, howeverthose containing mainly water are preferable. Further, the dispersionmedium is preferable to be properly mixed with a dispersant, a pHadjusting agent and the like.

[0039] Further, in a cerium-based abrasive of the present invention withdecreased coarse particles or magnetic particles, fluorine is properlyadded at the time of production if necessary to carry out chemicaltreatment.

BRIEF DESCRIPTION OF THE DRAWINGS

[0040]FIG. 1 shows a diagram illustrating the production steps of aconventional cerium-based abrasive. FIG. 2 shows a graph illustratingthe particle diameter distribution of a cerium-based abrasive relevantto First Embodiment measured by laser diffraction method.

[0041] Further, FIG. 3 is a diagram illustrating the coarse particleconcentration analysis relevant to the embodiment and FIG. 4 is adiagram illustrating the magnetic particle concentration analysisrelevant to the embodiment.

[0042]FIG. 5 is a schematic figure of the structure of a magnetic filterused for Second to Fourth Embodiments and FIG. 6 is a schematic figureof a magnet case used for Third Embodiment.

BEST MODE FOR CARRYING OUT THE INVENTION

[0043] Hereinafter, together with comparative examples, preferableexamples of the present invention will be described.

A. The Relation Between the Coarse Particle Concentration and thePolishing Property

[0044] First Embodiment

[0045] A slurry containing a powder with the average particle diameterof 0.9 μm (cumulative 50% particle diameter by micro-track method D50)was produced by pulverizing, for 5 hours, 2 kg of bastnasite concentratecontaining 70% by weight of TREO and 50% by weight of cerium oxidecontained in TREO in the presence of 2 liters of pure water with the useof a wet type ball mill (the capacity of 5 l) housing 12 kg of 5mm-diameter steel balls. The powder was treated with hydrochloric acidat a concentration of 1 mol/l and then washed with pure water andfiltered to obtain a cake. After that, the cake was dried and roasted at950° C. for 5 hours in a stationary furnace and after re-pulverized, theresulting powder was classified to obtain a cerium-based abrasive.

[0046] In the classifying step, classifying treatment was carried outonce using a dry type vertical wind classifying apparatus (trade name YMMicro Cut: manufactured by Yasukawa Electric Co., Ltd.) as a classifyingapparatus and setting the classification point at 7 μm.

[0047] Regarding the abrasive produced in such a manner was subjected toinvestigations of the average particle diameter and the particlediameter distribution by a laser diffraction method, which is aconventional inspection method, to find the abrasive having the averagediameter of 0.9 μm (cumulative 50% particle diameter by micro-trackmethod D50 ) and the particle diameter distribution shown as FIG. 2.According to the particle size distribution, no particles with 10 μm orhigher were detected.

[0048] In order to quantify the coarse particle concentration of theabrasive, analysis of the coarse particle concentration was carried outby the steps shown in FIG. 3. The analysis method of the coarse particleconcentration will be described along with FIG. 3.

[0049] (a) At first, 200 g of a cerium-based abrasive was measured andsampled and dispersed in a 0.1% sodium hexametaphosphate solution andstirred for 2 minutes to obtain a slurry.

[0050] (b) Next, the slurry was filtered through a micro sieve with apore diameter of 10 μm and the remaining on the sieve was recovered.

[0051] (c) Then, the recovered remaining was dispersed again in a 0.1%sodium hexametaphosphate solution to obtain a slurry. At that time,dispersion was carried out by ultrasonic stirring for 1 minute. Theslurry was then filtered through a micro sieve with pore diameter of 10μm.

[0052] (d) Further, the recovery of the remaining, the repeatedproduction of the slurry, and filtration were carried out twice in thepresent embodiment.

[0053] (e) Finally, the recovered coarse particles were sufficientlydried and then weighed.

[0054] Based on the analysis results of the coarse particleconcentration, 200 mg of coarse particles were sampled from thecerium-based abrasive produced in this embodiment and the coarseparticle concentration was found to be 1000 ppm (by weight).Consequently, the cerium-based abrasive produced in the presentembodiment was found containing coarse particles even though theircontent was as slight as 1000 ppm, although coarse particles with 10 μmor large size were not detected by a laser diffraction method, which isconventionally commonly employed.

[0055] Next, the specific surface area of abrasive particles of thecerium-based abrasive produced in the present embodiment was measured.The specific surface area was measured as follows. A sufficiently driedsample (an abrasive) in about 0.5 g was weighed and the surface area wasmeasured with a surface area measurement apparatus (a full-automaticsurface area measurement apparatus; Multisorp 12: manufactured by YuasaIonics Co., Ltd.). The measurement conditions were as follows: after thetesting apparatus was evacuated and using a gas mixture of nitrogen andhelium as an adsorption gas, the relative pressure was set 0.3 and theentire surface area of the sample was measured by a BET single pointmethod and the specific surface area was calculated from the sampleweight.

[0056] Second to Eighth Embodiments

[0057] Next, cerium-based abrasives with different coarse particlesconcentrations were produced with the classification points and thenumber of the classification times as shown in Table 1 changed while theproduction conditions of the raw material compositions and the roastingtemperature and the like being kept as same as those in First Embodimentand the coarse particle concentrations were analyzed. In Table 1, theterm, drying type, means those subjected to classification by the samevertical wind classifying apparatus as that of First Embodiment and theterm, wet type, means those subjected to classification by making thepowders after cake pulverization be 5% by weight of slurries andclassifying the slurries by a liquid cyclone.

[0058] Ninth Embodiment

[0059] In this embodiment, the raw material used was same as those usedfor First to Eighth Embodiments and the roasting conditions in theroasting step were set to be 1,000° C. and 5 hours. Other productionconditions were made same as those of First to Eighth Embodiments. Theclassifying conditions were controlled to be same as those of ThirdEmbodiment.

[0060] Tenth Embodiment

[0061] In this embodiment, the raw material used was same as those usedfor First to Eighth Embodiments and the roasting conditions in theroasting step were set to be 800° C. and 5 hours. Other productionconditions were made same as those of First to Eighth Embodiments. Theclassifying condition was controlled as to carry out classification onceat 10 μm classification point.

[0062] Eleventh Embodiment

[0063] In this embodiment, the raw material used was same as those usedfor First to Eighth Embodiments and the roasting conditions in theroasting step were set to be 700° C. and 5 hours. Other productionconditions were made same as those of First to Eighth Embodiments. Theclassifying condition was controlled as to carry out classification onceat 7 μm classification point.

[0064] Twelfth Embodiment

[0065] In this embodiment, the raw material used was same as those usedfor First to Eighth Embodiments and the roasting conditions in theroasting step were set to be 1,100° C. and 10 hours. Other productionconditions were made same as those of First to Eighth Embodiments. Theclassifying condition was controlled as to carry out classificationtwice at 7 μm classification point.

[0066] Thirteenth Embodiment

[0067] In this embodiment, the raw material used was same as those usedfor First to Eighth Embodiments and the roasting conditions in theroasting step were set to be 550° C. and 10 hours. Other productionconditions were made same as those of First to Eighth Embodiments. Theclassifying condition was controlled as to carry out classification onceat 7 μm classification point.

[0068] Fourteenth Embodiment

[0069] In this embodiment, an abrasive was produced by using a rareearth oxide as an abrasive raw material in place of the bastnasiteconcentrate and adding a fluorine component by carrying out treatmentwith ammonium fluoride. A slurry containing 2 kg of the rare earth oxidecontaining 99% by weight of TREO which was produced by roasting rareearth carbonates, the TREO containing 60% by weight of cerium oxide, wasmixed with 2 l of pure water. The resultant slurry was pulverized for 5hours with the use of a wet type ball mill (the capacity of 5 l) housing12 kg of 5 mm-diameter steel balls to obtain a slurry containing apowder with the-average particle diameter of 0.9 μm (cumulative 50%particle diameter by micro-track method D50). An ammonium fluoridesolution of 1 mol/l concentration was added to the slurry and afterwashing with pure water, the resulting slurry was filtered to obtain acake. After that, the cake was dried and then roasted at 950° C. for 5hours and after re-pulverized, the resulting powder was classified toobtain a cerium-based abrasive.

[0070] In this case, in the classifying step, classifying treatment wascarried out twice using the same dry type vertical wind classifyingapparatus as that employed for First Embodiment while the classificationpoint being set at 7 μm.

[0071] Fifteenth Embodiment

[0072] In this embodiment, using cerium oxide (99%) produced fromPaotau, China as an abrasive raw material, an abrasive was produced bycarrying out treatment with ammonium fluoride in the same manner asNinth Embodiment. While the mixing amounts of the raw material and waterand the pulverization conditions are controlled to be same as those inNinth Embodiment, the wet pulverization was carried out to obtain aslurry containing a powder with the average particle diameter of 1.4 μm(cumulative 50% particle diameter by micro-track method D50). Then,after fluoridation treatment and drying were carried out in the samemanner as those of Ninth Embodiment, roasting, pulverizing, andclassifying steps were carried out to obtain a cerium-based abrasive.

[0073] In this case, in the classifying step, classifying treatment wascarried out twice using the same dry type vertical wind classifyingapparatus as that employed for First Embodiment while the classificationpoint being set at 7 μm.

[0074] These abrasives produced in Second to Twelfth Embodiments werefound to contain no coarse particle with the size of 10 μm or larger bythe particle size distribution inspection by laser beam diffraction justthe same as First Embodiment, but existence of coarse particles in 150to 1,000 ppm (by weight) was found under the coarse particleconcentration analysis in the above described First Embodiment. Themeasurement results of these coarse particle concentration are shown inTable 1. As a result, the coarse particle concentrations were founddecreasing by making the classification point small and increasing thenumber of times of classification. Further, no difference was found inthe effect to decrease the coarse particles concentrations depending onthe models; either dry way or wet way; of classifying apparatuses.Incidentally, Table 1 shows the measurement values of specific surfacearea together. TABLE 1 Coarse particle Specific ClassificationClassification Times of concentration surface area type point (μm)classification (ppm) (m²/g) Second Embodiment dry way 7 twice 500 2.90Third Embodiment dry way 5 once 300 2.93 Fourth Embodiment dry way 5twice 150 2.95 Fifth Embodiment wet way 7 once 1000 2.86 SixthEmbodiment wet way 7 twice 500 2.90 Seventh Embodiment wet way 5 once300 2.92 Eighth Embodiment wet way 5 twice 150 2.97 Ninth Embodiment dryway 5 once 560 1.52 Tenth Embodiment dry way 10 twice 470 8.33 EleventhEmbodiment dry way 7 once 180 15.2 Twelfth Embodiment dry way 7 twice760 0.61 Thirteenth dry way 7 once 270 35.7 Embodiment Fourteenth dryway 7 twice 400 2.90 Embodiment Fifteenth Embodiment dry way 7 twice 5002.88

[0075] In contrast with the above described embodiments, as comparativeexamples, cerium-based abrasives were produced by changing theproduction conditions (the roasting condition and the classifyingcondition) as follows and their coarse particle concentrations andspecific surface areas were measured.

Comparative Example 1

[0076] In this comparative example, a cerium-based abrasive was producedin the same production method as Third Embodiment except that theclassification point was set to be 20 μm and its coarse particleconcentration was analyzed.

Comparative Example 2

[0077] In this comparative example, the same raw material as that usedin First to Eighth Embodiments was used and the roasting conditions wereset to be 1,100° C. and 10 hours. Other conditions were same as those inFirst to Eighth Embodiments. Further, classification point and thenumber of repeated classification times were respectively set to be 18μm and twice.

Comparative Example 3

[0078] In this comparative example, the same raw material as that usedin First to Eighth Embodiments was used and the roasting conditions wereset to be 550° C. and 10 hours. Other conditions were same as those inFirst to Eighth Embodiments. Further, classification point and thenumber of repeated classification times were respectively set to be 30μm and once.

Comparative Example 4

[0079] In this comparative example, the same raw material as that usedin First to Eighth Embodiments was used and the roasting conditions wereset to be 1,200° C. and 10 hours. Other conditions were same as those inFirst to Eighth Embodiments. Further, classification point and thenumber of repeated classification times were respectively set to be 16μm and twice.

[0080] Also in these abrasives by the comparative examples, no existenceof coarse particles of 10 μm or larger was found just like First toTwelfth Embodiments by the particle distribution inspection by the laserbeam diffraction, however, existence of coarse particles in 1,500 ppm(by weight) were confirmed by the coarse particle concentration analysisaccording to the present invention.

[0081] Next, using the cerium-based abrasives produced in First toTwelfth Embodiments and comparative examples 1 to 3, a glass materialwas polished and the polished state was compared and evaluated. Atfirst, the respective abrasives were dispersed in water to produceabrasive slurries of 10% by weight. The abrasive slurries wereconstantly being stirred to prevent the abrasives from precipitatingduring the polishing test by a stirring apparatus.

[0082] Using an Oscar type polishing tester (HSP-21 model, manufacturedby Taito Seiki Co., Ltd.) as the tester, the polishing of the glassmaterial was performed practically for glass for a flat panel of 60 mmφas an object to be polished by a polishing pad made of polyurethane. Thepolishing conditions were as follows: each abrasive slurry was suppliedat 500 ml/min; the pressure to the polished face was set to be 100g/cm²; the rotation speed of the polishing apparatus was set at 180 rpm;and the polishing duration was 3 minutes. The glass material after thepolishing was washed with pure water and dried in dust-free condition.

[0083] The measurement of the polishing values in an evaluation test wascarried out in the manner that the weight loss by polishing wascalculated by measuring the weight of the glass before and afterpolishing and while the weight loss in the case of using the abrasive ofthe comparative example 1 was defined to be 100, the polishing values ofabrasives other than the abrasive of the comparative example 1 weredefined as the values relative to 100. The evaluation of the surfacefinishing of the polished face was done on bases of the existence of thescratches in the polished surface. Practically, the evaluation wascarried out by radiating light of 300,000 lux from a halogen lamp to thesurface of the glass after polishing and observing the glass surface bya reflection method. In this case, the evaluation of the scratches wascarried out by giving marks based on the degree (the size) of scratchesand the number of the scratches and subtracting the marks from 100, themaximum. The evaluation results were shown in Table 2. TABLE 2Evaluation of Coarse particle Specific surface Polishing polished faceconcentration area (m²/g) value Marks Evaluation First Embodiment 1000ppm 2.87 100 85 Δ Second Embodiment 500 ppm 2.90 99 95 ∘ ThirdEmbodiment 300 ppm 2.93 99 97 ⊚ Fourth Embodiment 150 ppm 2.95 98 99 ⊚Fifth Embodiment 1000 ppm 2.86 100 87 Δ Sixth Embodiment 500 ppm 2.90100 95 ∘ Seventh Embodiment 300 ppm 2.92 99 98 ⊚ Eighth Embodiment 150ppm 2.97 99 99 ⊚ Ninth Embodiment 560 ppm 1.52 117 91 ∘ Tenth Embodiment470 ppm 8.33 91 98 ⊚ Eleventh Embodiment 180 ppm 15.2 75 98 ⊚ TwelfthEmbodiment 760 ppm 0.61 155 80 Δ Thirteenth 270 ppm 35.7 32 99 ⊚Embodiment Fourteenth 400 ppm 2.90 99 96 ⊚ Embodiment FifteenthEmbodiment 500 ppm 2.88 100 95 ∘ Comparative example 1500 ppm 2.84 10075 x 1 Comparative example 1500 ppm 0.60 153 59 x 2 Comparative example1800 ppm 35.9 33 77 x 3 Comparative example 1700 ppm 0.29 195 10 x 4

[0084] According to the results, regarding the abrasives of First toTwelfth Embodiments, following the decrease of the coarse particleconcentration, both of the number and the size of the scratches weredecreased and good polished faces were confirmed. Also, regarding thepolishing values, every one of the abrasives had the value approximatelysame as those of conventional cerium-based abrasives of comparativeexamples and even if the quantity of coarse particles was decreased, thepolishing speed was not decreased and consequently, a high polishingefficiency was found being maintained.

[0085] On the other hand, in comparison with the comparative examples,the abrasives of the comparative examples 1, 2, 4 had relatively goodpolishing values but the evaluation of the polished faces was low sinceformation of scratches was observed. That was attributed to that thecoarse particle concentration was high. Further, regarding the abrasiveof the comparative example 3, in addition to a low evaluation of thepolished face, the polishing value was also low. That was supposedlyattributed to that the specific surface area of the abrasive particleswas too low in addition to the high coarse particle concentration.

B. Relation Between the Magnetic Particle Concentration and thePolishing Property

[0086] Sixteenth Embodiment

[0087] A slurry was produced by mixing 10 kg of bastnasite concentratecontaining: 70% by weight of TREO; and 50% by weight of cerium oxidecontained in TREO with water in a proper amount as to have the slurryconcentration of 1,000 g/l, and the slurry was pulverized for 4 hourswith the use of a wet type pulverizer employing 3 mm-diameter zirconiapulverization medium to obtain a raw material slurry containing powderswith the average particle diameter of 0.9 μm. The resulting raw materialslurry was treated with hydrochloric acid of 1 mol/l concentration andwashed with pure water and then filtered to obtain a cake. After that,the cake was dried and roasted at 850° C. for 4 hours in a stationaryfurnace and after pulverization by an atomizer, the resulting powder wasclassified to obtain a cerium-based abrasive having the average of 0.9μm (cumulative 50% particle diameter by micro-track method D50).

[0088] In order to measure the magnetic particle concentration of theabrasive, analysis of the magnetic particles concentration was carriedout by the steps shown in FIG. 4 as one embodiment of the analysismethod of the magnetic particles concentration according to the presentinvention.

[0089] (a) At first, 500 g of a cerium-based abrasive was measured andsampled and dispersed in 1.5 l of water and further mixed with sodiumhexametaphosphate as a dispersant and stirred for 30 minutes to obtain aslurry.

[0090] (b) Next, a magnet with magnetic flux density of 2.0 T wasimmersed in the resulting slurry for 30 minutes. After 30 minutes, themagnet was taken out and adhering matter was recovered.

[0091] (c) Then, the recovered adhering matter was dispersed again in anaqueous sodium hexametaphosphate solution in the same manner to obtain aslurry, and a magnet with magnetic flux density of 2.0 T was immersed inthe slurry for 30 minutes in the same manner.

[0092] (d) Further, the steps of repeatedly making the slurry andimmersing a magnet were repeated 5 times to recover magnetic particles.

[0093] (e) The recovered magnetic particles were sufficiently dried andthen weighed.

[0094] Based on the analysis results, 250 mg of magnetic particles weresampled from the cerium-based abrasive produced in this embodiment andthe magnetic particles concentration was found to be 500 ppm (byweight).

[0095] Next, three types of cerium-based abrasives with differentmagnetic particle concentrations were produced by the operation asdescribed below and the magnetic particle concentration was analyzed.Incidentally, the production conditions were kept same as those of FirstEmbodiment, except the raw material compositions and the classifyingconditions of such as the roasting temperature.

[0096] Incidentally, filtration by a magnetic filter in the steps to beillustrated hereinafter was carried out for removing magnetic particlesby attaching a magnetic filter 1 as shown in FIG. 5 to the slurry pipeafter pulverization. In FIG. 5, the slurry 10 after pulverization wasintroduced into a lower part pipe 11 of the magnetic filter 1 and themagnetic particles were removed by being filtered through the magnetizedfilter 12. The filter 12 was magnetized by utilizing the magnetic fieldgenerated by exciting the electromagnetic coils 14 surrounding thecircumference. After that, a slurry 10′ from which magnetic particleswere removed was discharged out through an upper part pipe 13 and was tobe sent to the steps thereafter.

[0097] Further, FIG. 6 was a schematic illustration of a magnet case 15.The magnet case 15 comprised a plurality of rod magnets 17 between twometal plates 16, 16′ and was employed to remove magnetic particles in anabrasive raw material by passing the abrasive through rod magnets afterroasting and pulverization steps.

[0098] Seventeenth Embodiment

[0099] The raw material slurry produced by the same method as that ofSixteenth Embodiment was pulverized using a pulverization medium made ofa wear resistant steel with the diameter of 3 mm and the slurry afterpulverization was passed through a magnetic filter (magnetic fluxdensity 0.65 T and pore diameter 3 mm). After that, in the same steps asthose of First Embodiment, roasting, pulverizing, and classifyingtreatment was carried out to produce a cerium-based abrasive.

[0100] Eighteenth Embodiment

[0101] The raw material slurry produced by the same method as that ofSixteenth Embodiment was pulverized using a pulverization medium made ofa wear resistant steel with the diameter of 3 mm and the slurry afterpulverization was passed through a magnetic filter same as that ofSecond Embodiment. After that, in the same steps as those of FirstEmbodiment, after roasting and pulverizing treatment, the powder waspassed through a magnet case and then classified to produce acerium-based abrasive.

[0102] Nineteenth Embodiment

[0103] In this embodiment, an abrasive was produced by using a rareearth oxide as the abrasive raw material in place of the bastnasiteconcentrate and adding a fluorine component by carrying out ammoniumfluoride treatment. A slurry containing 2 kg of the rare earth oxidecontaining 99% by weight of TREO which was produced by roasting rareearth carbonates, the TREO containing 60% by weight of cerium oxide, wasmixed with 2 l of water. The resultant slurry was pulverized for 5 hourswith the use of a wet type ball mill pulverizer (the capacity 5 l)filled with 12 kg of 5 mm-diameter pulverization medium made of a steelwith and the resulting slurry after pulverization was passed through themagnetic filter. Then, the resulting slurry was mixed with an ammoniumfluoride solution in 1 mol/l concentration and washed with pure waterand filtered to obtain a cake. After that, the cake was dried and thenroasted at 850° C. for 4 hours in a stationary furnace and afterpulverization by an atomizer, the resulting powder was classified toobtain a cerium-based abrasive having the average of 0.9 μm (cumulative50% particle diameter by micro-track method D50).

[0104] The cerium-based abrasives produced in these Sixteenth toNineteenth Embodiments were found having the magnetic particleconcentration within a range from 150 to 1,000 ppm (by weight) by thesame analysis method of the magnetic particle concentration as FirstEmbodiment.

Comparative Example 5

[0105] In contrast with the above described Sixteenth to NineteenthEmbodiments, a cerium-based abrasive was produced by a conventionalproduction method. That is, an abrasive was produced using a wearresistant steel as a pulverization medium material for the slurrypulverization without a step of passing through either a magnetic filteror a magnetic case. After that, the magnetic particle concentration wasanalyzed by the same method as the above described embodiments.

[0106] Consequently, it was found that the cerium-based abrasiveaccording to the comparative example contained the magnetic particles in2,000 ppm (by weight) magnetic particle concentration.

[0107] Using the cerium-based abrasives produced by the above describedSixteenth to Nineteenth Embodiments and the comparative example 5 wereused for polishing glass materials and the polished state wascomparatively evaluated. The method for the polishing test as same asthose carried out in First to Fifteenth Embodiments. The evaluationresults were shown in Table 3. TABLE 3 Evaluation of Magnetic Specificsurface Polishing polished face concentration area (m²/g) value MarksEvaluation Sixteenth Embodiment 500 ppm 5.10 100 95 ∘ Seventeenth 1000ppm 5.02 100 85 Δ Embodiment Eighteenth Embodiment 300 ppm 5.14 100 98 ⊚Nineteenth Embodiment 150 ppm 5.20 100 98 ⊚ Comparative example 5 2000ppm 4.99 100 75 x

[0108] According to the results, regarding the abrasives of Sixteenth toNineteenth Embodiments, in comparison with the comparative example 5,following the decrease of the magnetic particle concentration, both ofthe number and the size of the scratches were decreased and goodpolished faces were confirmed. Also, regarding the polishing values,every one of the abrasives had the value approximately same as those ofconventional cerium-based abrasives of comparative examples and even ifthe quantity of magnetic particles was decreased, the polishing speedwas not decreased and consequently, a high polishing efficiency wasfound being maintained.

Industrial Applicability

[0109] A cerium-based abrasive according to the present application inwhich the coarse particle concentration and the magnetic particleconcentration are decreased is capable of forming a polished face withhigh precision and free of scratch formation. Especially, thecerium-based abrasive is usable even for forming a polished face of arecording medium such as a hard disk and the like and a substrate of aLCD and :the like for which high density and high precision are furtherrequired in the future.

[0110] Further, the cerium-based abrasive is excellent in the polishingvalue by controlling the specific surface area of the abrasive particlesto be within a specified range and, consequently, is more effective toform a polished face at a high polished value and high precision, whichis the intrinsic property of the cerium-based abrasive. Such acerium-based abrasive can be produced without requiring considerablealteration of a conventional production method.

1. A cerium oxide-based abrasive containing cerium oxide as a maincomponent and having an average particle diameter of 0.2 to 3.0 μm,wherein the cerium oxide-based abrasive contains coarse particles with aparticle diameter of 10 μm or larger in a concentration of 1,000 ppm orlower (by weight).
 2. The cerium-based abrasive according to claim 1,wherein of the concentration of the coarse particles with a particlediameter of 10 μm or larger is 300 ppm or lower (by weight) .
 3. Acerium oxide-based abrasive containing cerium oxide as a main componentand having an average particle diameter of 0.2 to 3.0 μm, wherein thecerium oxide-based abrasive contains magnetic particles in aconcentration of 1,000 ppm or lower (by weight).
 4. The cerium-basedabrasive according to claim 1, wherein the concentration of the magneticparticles is 300 ppm or lower (by weight).
 5. The cerium-based abrasiveaccording to any one of claims 1 to 4, wherein an average value of aspecific surface area of the abrasive particles is 0.5 to 30 m²/g.
 6. Aproduction method for a cerium-based abrasive comprising the steps ofproducing a slurry by mixing an abrasive raw material and a dispersionmedium, wet-pulverizing the abrasive raw material by treating the slurrywith a wet type pulverizer, roasting the abrasive raw material subjectedto the pulverization after filtration and drying, and carrying outclassification treatment for the abrasive raw material subjected to theroasting after dry pulverization, wherein the classification treatmentis carried out by controlling a classification point in a range from 0.5to 15 μm.
 7. The production method of the cerium-based abrasiveaccording to claim 6, wherein the method further comprises a step ofrepeatedly at least once classifying the abrasive subjected to theclassification treatment.
 8. A production method for a cerium-basedabrasive comprising the steps of producing a slurry by mixing anabrasive raw material and a dispersion medium, wet-pulverizing theabrasive raw material by treating the slurry with a wet type pulverizer,roasting the abrasive raw material subjected to the pulverization afterfiltration and drying, and carrying out classification treatment for theabrasive raw material subjected to the roasting after dry pulverization,wherein the method further comprises a step of passing the slurrytreated by the wet type pulverizer through a filter made of a magneticmaterial magnetized by excitation.
 9. The production method of thecerium-based abrasive according to claim 8, wherein the filter made ofthe magnetic material is magnetized in a magnetic flux density range of0.1 to 2.0 T to pass the slurry through.
 10. A production method for acerium-based abrasive comprising the steps of producing a slurry bymixing an abrasive raw material and a dispersion medium, wet-pulverizingthe abrasive raw material by treating the slurry with a wet typepulverizer, roasting the abrasive raw material subjected to thepulverization after filtration and drying, and carrying outclassification treatment for the abrasive raw material subjected to theroasting after dry pulverization, wherein the abrasive raw material iswet pulverized using a pulverization medium made of a non-magneticmaterial as a pulverization medium to be packed in the wet typepulverizer.
 11. The production method of the cerium-based abrasiveaccording to claim 10, wherein zirconia or alumina is used as thenon-magnetic material constituting the pulverization medium.
 12. Aproduction method for a cerium-based abrasive comprising the steps ofproducing a slurry by mixing an abrasive raw material and a dispersionmedium, wet-pulverizing the abrasive raw material by treating the slurrywith a wet type pulverizer, roasting the abrasive raw material subjectedto the pulverization after filtration and drying, and carrying outclassification treatment for the abrasive raw material subjected to theroasting after dry pulverization, wherein the method further comprises astep of passing the abrasive raw material subjected to the roastingnearby a tubular body, a plate-like body, or a rod-like body made of amagnetized magnetic material.
 13. The production method of thecerium-based abrasive according to claim 12, wherein the tubular body,the plate-like body, or the rod-like body made of the magnetic materialis magnetized in the magnetic flux density within a range from 0.1 to2.0 T to pass the slurry through.